Continuous Hot-Dip Galvanized Thin Steel Sheets and Steel Strips
Hot-dip galvanizing is the process of coating steel with a thin layer of zinc using a bath of molten zinc. The process has been in use since ancient times to protect iron and steel from corrosion. GB 2518-88 specifies the requirements and test methods applicable to continuous hot-dip galvanized thin steel sheets and steel strips. The requirements and test methods specified by this standard apply to both flat and corrugated, hot-dip galvanized steel sheets and strips with a thickness of 0.2mm to 3mm.
The Standard requires galvanized steel sheets and strips to meet the requirements of chemical composition, tensile strength, elongation, and coating thickness. The chemical compositions and mechanical properties of galvanized steel sheets and strips should conform to the requirements specified in the following table.
Steel grade Designation Chemical composition (%) Tensile strength (MPa) Yield point (MPa) Elongation (%) Q201 A C 0.06 max Si 0.03 max Mn 0.65-1.35 P 0.02 max S 0.015 max N 0.012 max Cu 0.2 max 270-380 210 min 25 min Q202 B C 0.08 max Si 0.03 max Mn 0.85-1.3P 0.02 max S 0.015 max N 0.012 max Cu 0.25 max 270-440 235 min 25 min Q203 C C 0.08 max Si 0.03 max Mn 0.85-1.3 P 0.02 max S 0.015 max N 0.012 max Cu 0.25 max 270-490 280 min 25 min
The standard also requires the galvanized steel sheets and strips to meet certain requirements regarding coating thickness. Coating thickness is an important indicator of the quality of the galvanized process, as a thicker coating yields better corrosion resistance. The average coating thickness required by the standard is 25μm on the front side and 15μm on the reverse side.
The standard requires galvanized steel sheets and strips to be tested for coating adhesion. Adhesion is an important quality factor when it comes to the performance of hot-dip galvanized sheet and strip products. The adhesion test method specified in this standard involves a cross-cut test, in which scratching is made on the test sample and then scratched with a metal wire brush. The coating should remain intact and should not be peeled off with the metal wire brush.
In addition to the requirements and test methods specified above, the standard also specifies requirements and test methods for marking, packaging and storage of galvanized steel sheets and strips. The standard requires galvanized steel products to be marked with their source of origin, steel grade and coating thickness on each sheet. It also requires the packaging material to be moisture-proof, and to ensure that the galvanized products are stored in a dry place.
In conclusion, GB 2518-88 is the Chinese national standard that specifies the requirements and test methods applicable to continuous hot-dip galvanized thin steel sheets and steel strips. The standard provides requirements for the chemical compositions, mechanical properties, coating thickness, adhesion tests, and marking, packaging, and storage for galvanized steel sheets and strips. Adherence to this standard helps ensure the quality of galvanized steel products.
